$f(x) = \begin{cases} 9 & \text{if } x = 0 \\ 2x^{2}+3 & \text{otherwise} \end{cases}$ What is the range of $f(x)$ ?
First consider the behavior for $x \ne 0$ Consider the range of $2x^{2}$ The range of $x^2$ is $\{\, y \mid y \ge 0 \,\}$ Multiplying by $2$ doesn't change the range. To get $2x^{2}+3$ , we add $3$ So the range becomes: $\{\, y \mid y ≥ 3 \,\}$ If $x = 0$ , then $f(x) = 9$ , which eliminates $f(x) = 3$ from the range. The new range is $\{\, y \mid y > 3 \,\}$.